1. Field of the Invention
The subject invention generally relates to a wetting additive and a coating composition including the wetting additive. More specifically, the subject invention relates to a wetting additive that is added to a coating composition to wet pigments for excellent color development, to wet the substrate for good coverage and reduced surface imperfections, and to add defoaming properties to the coating composition.
2. Description of the Prior Art
Coating compositions are well known in the art for use in various applications, especially in the construction industry for decorative and protective uses. The coating compositions are typically prepared by coloring or tinting a base composition at a point of purchase through addition of a pigment dispersion including organic and/or inorganic pigments. The base composition includes a polymeric base, such as acrylic latex, and may be water-borne or solvent-borne. Pigment dispersions are formulated for both water-borne and solvent-borne base compositions to be easily miscible and stable in the base composition.
A relative tint strength of the pigment dispersion, also known as color development, is one of the most important properties of the pigment dispersion. Tint strength is a function of a degree of dispersion of the pigment in the pigment dispersion and is a measure of color intensity. Specifically, more complete dispersion of the pigment within the pigment dispersion correlates to more intense color in the pigment dispersion and the resulting coating composition. As a result of more complete dispersion of the pigment, the pigment dispersion may be formulated with a lower pigment concentration to achieve desired tint strength as compared to pigment concentrations that are required when poorer dispersion of the pigment is achieved. Lower required pigment concentrations correlate to reduced cost of the pigment dispersion and resulting coating composition.
The pigment dispersions and/or coating compositions are formulated with additional additives in order to promote or hinder certain properties. For example, dispersing additives, also referred to as wetting additives, have been used as a key component to disperse the pigment in the coating composition and to provide acceptable color development. Conventional dispersing additives, such as allyl phenol ethoxylates (APEO), are used due to their effectiveness in wetting and dispersing particles and substrates. However, APEOs are under EPA regulatory scrutiny due to claimed aquatic toxicity and suspected estrogen-mimicking nature. Such concerns have led to a ban on the use of APEOs in coating compositions within the European Union and in parts of Canada. Therefore, many companies are re-formulating coating compositions or developing new coating compositions to eliminate the APEO dispersing additives. This is especially true for companies that export their coating compositions to countries where APEO is banned because most companies prefer to have one universal formulation that can be sold throughout the world rather than separate formulations for various parts of the world. However, APEOs are not easy to replace because of their effectiveness in wetting and dispersing properties. Further, the price of APEOs is low compared to other dispersing additives, and their cost-to-performance ratio is very attractive. While acetylenic diols have also been used in wetting and grind aid additives, there remains an opportunity to develop other wetting and grind aid additives that improve upon the performance of acetylenic diols.
Alcohol alkoxylates are one class of additives that are known for use in coating compositions. Alcohol alkoxylates cover a broad spectrum of additives that perform various functions, such as defoaming, wetting, dispersing, and acting as a surfactant. An example of one type of alcohol alkoxylate has the following formula:X(AO)nHwherein X is selected from the group of linear carbon chains, branched carbon chains, aromatic rings, and combinations thereof, AO is an allyleneoxy group selected from the group of ethyleneoxy groups, 1,2-propyleneoxy groups, 1,2-butyleneoxy groups, and combinations thereof, and n is from to 1 to 75. Such alcohol alkoxylates, when included in the coating compositions, are present for any of the functions as described above.
U.S. Pat. No. 6,582,505 to Bouvy et al. is one specific reference that discloses the use of branched alcohol alkoxylates in coating compositions. In particular, Bouvy et al. teaches that the specific branched alcohol alkoxylates disclosed therein are suitable for replacing APEOs, and that the branched alcohol alkoxylates provide coating compositions with comparable properties to the APEOs. Bouvy et al. also discloses that other linear alcohol alkoxylates may be used in conjunction with the branched alcohol alkoxylates. While all ethylene oxide is typically used to alkoxylate branched or linear alcohols to make the alcohol alkoxylates of Bouvy et al., block and random copolymers of ethylene oxide and propylene oxide are also disclosed. However, there is no recognized benefit in Bouvy et al. through the use of the specific branched and linear alcohol alkoxylates taught therein and, as shown in Example 3, column 12 of Bouvy et al., worse color acceptance is achieved when branched and linear alcohol alkoxylates are used as compared to coating compositions including only branched alcohol alkoxylates.
Due to the strong demand to develop viable alternatives to replace APEOs in pigment dispersions and coating compositions without sacrificing physical properties, there is an opportunity to provide a wetting or dispersing additive, and a composition including the wetting or dispersing additive, that further improves upon the existing replacements for APEOs.